In the late 1950’s, Harry Belafonte was on top of the world. In 1956, he had recorded the album Calypso—the first ever to sell over one million copies—and had ignited a Jamaican music craze. Awards, accolades, celebrity and its attendant glamour followed in spades.

But none of this was enough to impress a landlord on West End Avenue, who turned Mr. Belafonte down for an apartment in his stately building, which dated back to the turn of the century.

The singer-cum-activist fought back not with picket signs, but with the muscle celebrities give such a workout: money. He bought the entire 13-story building and converted it to a co-op two years later, attracting the likes of singer Lena Horne to take up residence there.

Now, after spending more than half his life on the building’s fifth floor, Mr. Belafonte has put his apartment on the market for $15 million. The 21-room spread—it has one of the largest floor plans on all of West End Avenue—could now change hands for the first time in 46 years.

The vast apartment includes eight bedrooms, eight bathrooms, a library, a poolroom and a laundry room.

Mr. Belafonte’s master bedroom features a sauna, while several of the other bedrooms include en suite baths and walk-in closets.

Artifacts and memorabilia collected over seven decades of a very momentous life can be found throughout the sprawling apartment. Works by artists Charles White and Diego Rivera adorn the walls, as well as handwritten correspondence from the likes of Eleanor Roosevelt and Martin Luther King Jr.

The Mexican-tiled gourmet kitchen includes two Sub-Zero refrigerators. Other features include high ceilings, wood floors and four wood-burning fireplaces.

Mr. Belafonte combined two units to form the palatial living space that is over 7,000 square feet. After joining the “A” and “B” lines, the entertainer could enjoy a rare vantage point, with exposures in all four directions. Also, there are two keyed elevators leading up to the apartment, so the lucky buyer can take his or her pick when returning home.

The prewar doorman building also has a garage (although the lengthy waiting list for a spot could last another 46 years).

A native New Yorker, Mr. Belafonte was born in Harlem, not far from the present apartment, in 1927, and at age 17 dropped out of high school to join the Navy. About a decade following the war (and after various other jobs), he received an RCA contract and started recording.

Singing, acting and composing aside, Mr. Belafonte has been involved in numerous causes, and lauded by many for his efforts as a UNICEF Goodwill Ambassador and work on civil-rights issues. However, Mr. Belafonte’s friendship with dictator Fidel Castro and his harsh 2002 critique of then–Secretary of State Colin Powell have won him numerous detractors, especially amongst conservatives.

Besides performing (and courting controversy), Mr. Belafonte has kept busy in the real-estate market, recently putting his oceanfront property in St. Martin on the market for $2.9 million, according to the New York Post. The 3.3-acre estate is located on Plum Beach, and features a four-bedroom house, a gardener’s cottage, caretaker’s cottage and pool.

Although he is selling his Upper West Side pad, the longtime New Yorker plans to remain in the city, according to a source close to the entertainer.

Mr. Belafonte could not be reached by press time.

Solomon R. Guggenheim Museum director Thomas Krens, who recently listed his sun-drenched Tribeca penthouse for $5.5 million, has abruptly taken it off the market.

On July 23, both the real-estate and art worlds were rocked with an entry on Modern Art Notes, critic Tyler Green’s much-read blog, which reported that Mr. Krens was selling his triplex apartment. But less than a week later the listing disappeared.

A Guggenheim spokesperson confirmed that Mr. Krens took the luxurious property off the market, but would not elaborate on the circumstances. The 4,450-square-foot condo had been listed with Amalia Ferrante of the Corcoran Group. Ms. Ferrante did not return calls for comment.

By putting his downtown residence on the market, Mr. Krens helped fuel rumors he was not long for the top position at the museum. The Guggenheim’s financial dealings became hot gossip after Vicky Ward’s recent 6,300-word Vanity Fair article documenting the battle among Guggenheim Foundation trustees over Mr. Krens’ tenure and future prospects.

Throughout his 17 years as the Guggenheim’s chief, Mr. Krens has been lent $1.5 million—interest free—from the foundation for his personal real-estate ventures. In 1988 and 1989, when the former Williams College art-history professor first arrived in New York, Mr. Krens was given a total of $1 million toward a Fifth Avenue apartment, with an additional $500,000 given 10 years later toward the purchase of his Tribeca home.

In August 1999, Mr. Krens and his wife, designer Susan Lyons, purchased the downtown penthouse for $2.35 million. Mr. Krens and Ms. Lyons still owe the entire $1.5 million borrowed from the foundation, according to March 2005 mortgage records obtained by The Observer.

Before buying the Warren Street apartment, Mr. Krens had informed the board that a larger place was needed to entertain properly, according to The Chronicle of Philanthropy.

With a 50-foot-wide main floor and 22-foot-tall ceilings with huge skylights, it is the ideal place to party (and extract money from wealthy patrons of the arts). The living area includes six large windows and a wood-burning fireplace.

The dining room (complete with Frank Gehry-designed chairs) seats at least 20, and light enters through yet another skylight. For all those starving art dealers, there is both a chef’s kitchen and a service kitchen.

Besides the ample party space, there are four bedrooms and three and a half bathrooms. On the second floor is Mr. Krens’ master suite, with adjacent bath. On the third level, there is a studio with a skylight and a 900-square-foot terrace with superb views.

If Mr. Krens puts his apartment back on the market, he could double his investment after only six years. That’s pretty good, and far better than the foundation, which by providing an interest-free loan, will end up losing money on the transaction.

Park Slope

431 Seventh Street

Two-and-half-bedroom, two-bathroom co-op.

Asking: $1.5 million. Selling: $1.5 million.

Charges: $750.

Time on the market: three months.

EMPTY NEST EGG With the kids grown up, this retired couple decided to move to their country house. So there was no reason to hold onto their cherished duplex co-op in Park Slope. The 20-foot-wide and 60-foot-deep brownstone includes high ceilings, a fireplace, bay windows, skylights, hardwood floors and exposed brick. “It retained a lot of the prewar detail but had been completely gut-renovated,” said Tracey McLean of the Corcoran Group, who represented the buyers and sellers with her colleague, Patricia Neinast. In addition to the prewar charm, the 2,200-square-foot apartment includes a modern kitchen with stainless-steel appliances and granite countertops. It took only one open house to attract the buyers, with about 20 parties coming to ogle the loft-like space. A young couple purchased the apartment, paying the full asking price; the buyers are leaving behind the West Village for the quaint Brooklyn neighborhood where everyone seems to be pushing a stroller. But if they ever long for Manhattan, there’s a simple solution: The apartment features a 560-square-foot private roof deck that offers superb views of the Manhattan skyline.